linux-kernel - Re: iptables very slow after commit 784544739a25c30637397ace5489eeb6e15d7d49

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Date:	Fri, 10 Apr 2009 18:39:18 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>
cc:	shemminger@...tta.com, jeff.chua.linux@...il.com,
	dada1@...mosbay.com, jengelh@...ozas.de, kaber@...sh.net,
	r000n@...0n.net,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: iptables very slow after commit
 784544739a25c30637397ace5489eeb6e15d7d49



On Fri, 10 Apr 2009, David Miller wrote:
> 
> [ CC:'ing netfilter-devel and netdev... ]

I wonder if we should bring in the RCU people too, for them to tell you 
that the networking people are beign silly, and should not synchronize 
with the very heavy-handed

	synchronize_net()

but instead of doing synchronization (which is probably why adding a few 
hundred rules then takes several seconds - each synchronizes and that 
takes a timer tick or so), add the rules to be free'd on some rcu-freeing 
list for later freeing.

Or whatever. Paul? synchronize_net() just calls synchronize_rcu(), and 
with that knowledge and a simple

	git show 784544739a25c30637397ace5489eeb6e15d7d49

I bet you can already tell people how to fix their performance issue.

		Linus

---
> > On Fri, 10 Apr 2009 17:15:52 +0800 (SGT)
> > Jeff Chua <jeff.chua.linux@...il.com> wrote:
> >> 
> >> Adding 200 records in iptables took 6.0sec in 2.6.30-rc1 compared to 
> >> 0.2sec in 2.6.29. I've bisected down this commit.
> >> 
> >> There are a few patches on top of the original patch. When I reverted the 
> >> original commit + changing rcu_read() to rcu_read_bh(), it speeds up the 
> >> inserts back to .2sec again.
> >> 
> >> I'm loading all the firewall rules during boot-up and this 6 secs slowness 
> >> is really not very nice to wait for.
> > 
> > The performance benefit during operation is more important. The load
> > time is fixable. The problem is probably generic to any set of rules,
> > but could you post some info about your configuration (like the rule
> > set), and the system configuration (# of cpu's, config etc).
> > --
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